Munich-based chemicals company Wacker is launching a liquid silicone rubber for radiation-sterilisable silicone valves used in medical devices.

Devices for administering liquid medication often employ valves made from silicone elastomers, which offer high dosing accuracy, are biocompatible and can be readily sterilised on account of their resistance to heat, radiation and chemicals. However, sometimes the slits of these valves close up when radiation-sterilised and the higher the radiation dose, the more the slits close over. This can impair the dosing accuracy of the valve and may even cause it to fail. Consequently, valve manufacturers have so far resorted to a process auxiliary, which prevents opposing slit edges from touching and is applied to the edges of the slits as they are being created in the membrane.

Wacker says Silpuran 6610/40 allows such valves to be made without the use of additional auxiliaries. It is also so durable that the valve slits will not heal even when exposed to radiation doses far in excess of those usually employed in sterilisation.

This non-healing effect is the outcome of a special formulation of the liquid silicone rubber, which also allows the silicone valve membrane to be slit prior to post-curing. The valve slits can be created either with a suitable mould during injection moulding or with a punching die after demoulding.

Eliminating the need for a release agent makes it possible to produce silicone valves much more quickly, cleanly and inexpensively than previously, the firm says.

Valves made from Silpuran 6610/40 can be sterilised with ionising radiation prior to shipping, without suffering any loss of dosing accuracy.

The two-component white product is packaged in Wacker’s cleanrooms. It will be introduced at Compamed in Düsseldorf, Germany in November.